3 ms·

> The new study has thus determined that the Moon is significantly older than previously believed True enough, I suppose: ~50 million years vs ~150 million yea

> The new study has thus determined that the Moon is significantly older than previously believed True enough, I suppose: ~50 million years vs ~150 million years after solar system formation. But on the scale of ~4.5 billion years ago, that's not such a huge difference. And conversely, 50-100 million years is a long time in the context of stuff with solar orbits on the scale of 1-100 years. I'm guessing that formation of the Sun and solar system was a strongly exponential process. And the Moon probably formed during the final flurry of adjustments among major bodies.

squirrelicus 7y ago
Hahahaha. "Adjustments" is quite a way to describe it. I wonder how many large bodies exist today because an impact sightly nudged them from catastrophe to orbital stability. My arm chair astrophysics training tells me the answer is "literally all of them"
- kijin 7y ago
  Yeah, "Adjustments" would be an understatement of the billennium. According to recent theories I've read about, Jupiter may have veered inward within 1.5 AU of the Sun, crashing into everything and creating a massive debris field that is the asteroid belt. Meanwhile, Uranus and Neptune may have switched positions at some point. The solar system was a huge mess back then.
  - mirimir 7y ago
    True. So was it likely that it was this Jupiter incursion that sent the "Mars-size planet" to the Earth, creating the Moon? Also, I read somewhere, a few years ago, that the core of said "Mars-size planet" survived the collision, and ended up as Mercury. As I recall, part of the argument was that by composition, Mercury looks like a core, not a planet (not even a near-solar planet). And there perhaps was some isotopic evidence. Maybe also some compositional mass-balance argument like "'proto Earth' + 'Mars-size planet' <> Earth + Moon". There being missing iron etc.
    - kijin 7y ago
      The jumping Jupiter scenario is usually associated with the Late Heavy Bombardment, which is half a billion years too late for the age of the Moon estimated by OP. But of course there are disagreements about when Jupiter did its thing. There's a lot of variance in "Mars-sized", so I wouldn't count on an easily noticeable mass-balance match. Mars, Mercury, and the Moon are all very small compared to Earth. Earth is more massive than all of the other rocky planets and the Moon combined, and yes, that includes Venus.

squirrelicus 7y ago

Hahahaha. "Adjustments" is quite a way to describe it. I wonder how many large bodies exist today because an impact sightly nudged them from catastrophe to orbital stability. My arm chair astrophysics training tells me the answer is "literally all of them"

kijin 7y ago
Yeah, "Adjustments" would be an understatement of the billennium. According to recent theories I've read about, Jupiter may have veered inward within 1.5 AU of the Sun, crashing into everything and creating a massive debris field that is the asteroid belt. Meanwhile, Uranus and Neptune may have switched positions at some point. The solar system was a huge mess back then.
- mirimir 7y ago
  True. So was it likely that it was this Jupiter incursion that sent the "Mars-size planet" to the Earth, creating the Moon? Also, I read somewhere, a few years ago, that the core of said "Mars-size planet" survived the collision, and ended up as Mercury. As I recall, part of the argument was that by composition, Mercury looks like a core, not a planet (not even a near-solar planet). And there perhaps was some isotopic evidence. Maybe also some compositional mass-balance argument like "'proto Earth' + 'Mars-size planet' <> Earth + Moon". There being missing iron etc.
  - kijin 7y ago
    The jumping Jupiter scenario is usually associated with the Late Heavy Bombardment, which is half a billion years too late for the age of the Moon estimated by OP. But of course there are disagreements about when Jupiter did its thing. There's a lot of variance in "Mars-sized", so I wouldn't count on an easily noticeable mass-balance match. Mars, Mercury, and the Moon are all very small compared to Earth. Earth is more massive than all of the other rocky planets and the Moon combined, and yes, that includes Venus.